Gamma glutamyl transpeptidase

Gamma Glutamyl Transpeptidase

Gamma glutamyl transpeptidase (GGT), also known as gamma-glutamyl transferase, is an enzyme that plays a crucial role in the gamma-glutamyl cycle, which is involved in the metabolism of glutathione and the transfer of amino acids across the cellular membrane. GGT is predominantly found in the liver, kidney, and pancreas, and its activity is often measured in clinical settings as a marker of liver health.

Structure and Function

GGT is a membrane-bound enzyme that catalyzes the transfer of the gamma-glutamyl functional group from molecules such as glutathione to an acceptor, which may be an amino acid, a peptide, or water. This reaction is essential for the breakdown and resynthesis of glutathione, a critical antioxidant that protects cells from oxidative damage.

The enzyme is composed of two subunits, a heavy chain and a light chain, which are derived from a single polypeptide precursor. The active site of GGT is located in the light chain, where the gamma-glutamyl group is transferred.

Clinical Significance

GGT levels in the blood are commonly measured as part of liver function tests. Elevated GGT levels can indicate liver disease, bile duct obstruction, or alcohol abuse. It is often used in conjunction with other tests, such as alanine transaminase (ALT) and aspartate transaminase (AST), to assess liver function.

Liver Disease

In liver disease, such as hepatitis, cirrhosis, or liver cancer, GGT levels may be elevated due to increased enzyme production or release from damaged liver cells. GGT is particularly sensitive to changes in liver function and can be one of the first indicators of liver damage.

Alcohol Consumption

Chronic alcohol consumption can lead to elevated GGT levels. GGT is often used as a biomarker for alcohol use, as it can remain elevated for several weeks after alcohol consumption has ceased.

Measurement

GGT activity is measured in serum using a colorimetric assay, where the enzyme catalyzes the transfer of the gamma-glutamyl group from a substrate to an acceptor, resulting in a color change that can be quantified spectrophotometrically.

Also see

• Liver function tests
• Glutathione
• Alanine transaminase
• Aspartate transaminase
• Bilirubin